The present, invention relates to a metal surface-treating agent for such steel substrates as cold-rolled steel, hot-rolled steel, stainless steel, electroplated zinc-coated steel, hot-dip zinc coated-steel, zinc-aluminum alloy-coated steel, zinc-iron alloy-coated steel, zinc-magnesium alloy-coated steel, zinc-aluminum-magnesium alloy-coated steel, aluminum-coated steel, aluminum-silicon alloy-coated steel, tin-coated steel, lead-tin alloy coated steel, and chromium-coated steel, a surface-treating method, a method of producing coated steel materials further having top coatings on the treated surfaces, and coated steel products as produced by the method.
As the metallic surface treating agent, a chromium-containing surface-treating agent such as a chromate system or a phosphate-chromate system has heretofore been used broadly and still in use today. However, in view of the recent trend toward more stringent regulatory control for environmental protection, it is likely that the use of such coating systems will be restricted for fear of the toxicity, particularly carcinogenicity, of chromium. Therefore, development of a metallic surface-treating agent not containing chromium and yet as effective as the chromating agent in imparting adhesion and corrosion resistance has been awaited.
As disclosed in Japanese Patent Hei-11-29724, the inventors of the present invention previously developed a nonchromate rust-preventive agent comprising a water-based resin and, as incorporated therein, a thiocarbonyl group containing compound, a phosphate ion, and water-dispersible silica. Regrettably, however, this system was found to be inadequate for the above application which requires stringent processability and adhesion, although it provides good corrosion resistance. Meanwhile, with regard to silane coupling agents, an acidic surface-treating agent containing two dissimilar silane coupling agents is disclosed in Japanese Kokai Publication Hei-8-73775. However, this system is quite deficient in corrosion resistance for use in applications where high corrosion resistance and good processability are required after metallic surface treatment as in the present invention.
Moreover, Japanese Kokai Publication Hei-10-60315 discloses a steel structure surface-treating agent containing a silane coupling agent having a certain functional group reactive with a water-based emulsion but the corrosion resistance required here is only that of a degree satisfying comparatively mild test requirements such as those of a wet test and as far as corrosion-resistance is concerned, the system is a far cry from the rust inhibitor meeting the highly critical corrosion resistance requirements as provided by the present invention. With the foregoing state of the art by way of background, there has been a standing demand for development of a metallic surface-treating agent expressing sufficient corrosion resistance and processing adhesion at thin coating thicknesses.
The present invention has for its object to provide a nonchromate metallic surface-treating agent which is suited for metallic substrates, particularly metal-coated steel materials, and despite the absence of chromium therein, is capable of imparting high processability and corrosion resistance in preparation for a coating or other procedure.
The nonchromate metallic surface-treating agent according to the present invention comprises, in each liter thereof,
(a) 0.01 to 100 g/l of a silane coupling agent and/or a hydrolytic condensation product thereof,
(b) 0.05 to 100 g/l of water-dispersible silica (as solids), and
(c) 0.01 to 50 g/l, in terms of Zr ion, of a zirconium compound and/or 0.01 to 50 g/l, in terms of Ti ion, of a titanium compound and/or
(d) 0.01 to 100 g/l of a thiocarbonyl-containing compound and/or
(e) 0.1 to 100 g/l of a water-soluble acrylic resin.
The nonchroinate metallic surface-treating agent according to the present invention may comprise 0.01 to 100 g/l of phosphate ion.
The method of treating a metallic surface according to the present invention comprises treating the surface of a steel material or a metal-coated steel material with the above metallic surface-treating agent and said method is most suited for the surface treatment of zinc-coated steel material.
The surface-treated steel material and surface-treated metal-coated steel material according to the invention can be obtained by the above-method with-said metallic surface-treating agent.
The method of producing a coated steel material according to the present invention comprises treating the surface of a metal-coated steel material with said metallic surface-treating agent and, then, applying a top coat thereon.
The coated steel material of the present invention is obtainable by the above method using said metallic surface-treating agent.
As the silane compound as one of its essential components, the metallic surface-treating agent of the present invention comprises a silane coupling agent and/or a hydrolytic condensation product thereof. The hydrolytic condensation product of a silane coupling agent means an oligomer obtainable by hydrolytic polymerization of the silane coupling agent.
The silane coupling agent which can be used as above in the present invention is not particularly restricted but includes the following, among others: vinylmethoxysilane, vinyltrimethoxysilane, vinylethoxysilane, vinyltrimethoxysilane, 3-aminopropyltriethoxysi.lane, 3-glycidoxypropyltrimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane, N-(1,3-dimethylbutylidene)-3-(triethoxysilyl) -1-propanamine, N,Nxe2x80x2-bis[3-(trimethoxysilyl)propyl]ethylenediamine, N-(xcex2-aminoethyl)-xcex3-aminopropylmethyldimethoxysilane, N (xcex2-aminoethyl)-xcex3-aminopropyltrimethoxysilane, xcex3-aminopropyltrimethoxysilane, xcex3-aminopropyltriethoxysilane, xcex3-glycidoxypropyltrimethoxysilane, xcex3-glycidoxy-propyltriethoxysilane, xcex3-glycidoxypropylmethyl-dimethoxysilane, 2-(3,4-epQxycyclohexyl) ethyl-trimethoxysilane, xcex3-methacryloxypropyltrimethoxysilane, xcex3-methacryloxypropyltriethoxysilane, xcex3-mercaptopropyltrimethoxysilane, xcex3-mercaptopropyl-triethoxysilane and N-[2-(vinylbenzylaminolethyl]-3-aminopropyltrimethoxysilane.
The particularly preferred silane coupling agent includes vinylmethoxysilane, vinylethoxysilane, 3-aminopropyltriethoxysilane, 3-glycidoxypropyl-trimethoxysilane, 3-methacryloxypropyltriinethoxysilane, 3-mercaptopropyltriinethoxysilane, N-(1,3-dimethylbutylidene)-3-(triethoxysilyl)-1-propanamine and N,Nxe2x80x2-bis[3-(trimethoxysilyl)propyl]ethylenediamine. These silane coupling agents can be used each alone or in a suitable combination.
In the present invention, said silane compound is formulated in a concentration of 0.01 to 100 g/l, preferably 0.05 to 25 g/l, in each liter of the metallic surface-treating agent. If the concentration of the silane compound is less than 0.01 g/l, the corrosion resistance-improving effect as well as the effect of improving adhesion to the nonchromate primer will be insufficient, while the use of the silane compound in excess of 100 g/l will result in saturation of the effect of addition and be uneconomical.
The metallic surface-treating agent of the present invention comprises water-dispersible silica. The water-dispersible silica which can be used is not particularly restricted but is preferably spherical silica, chainlike silica or aluminum-modified silica, which is lean in sodium and other impurities and weakly basic. The spherical silica includes colloidal silica such as xe2x80x9cSnowtex Nxe2x80x9d, xe2x80x9cSnowtex UPxe2x80x9d (both manufactured by Nissan Chemical) and fumed silica such as xe2x80x9cAerosilxe2x80x9d (Japan Aerosil); the chainlike silica includes silica gel such as xe2x80x9cSnowtex PSxe2x80x9d (Nissan Chemical); and the aluminum-modified silica includes xe2x80x9cAdelite AT-20Axe2x80x9d (Asahi Denka), all of which are commercially available.
The above water-dispersible silica is formulated in a concentration of 0.05 to 100 g/l, preferably 0.5 to 60 g/l, in each liter of the metallic surface-treating agent on a solid basis. If the concentration of water-dispersible silica is less than 0.05 g/l, the corrosion resistance-improving effect will be insufficient, while the use of silica in excess of 100 g/l will not be rewarded with any further improvement in corrosion resistance but rather detract from the bath stability of the metallic surface-treating agent.
The metallic surface-treating agent of the present invention further comprises a zirconium compound and/or a titanium compound. The zirconium compound includes zirconyl ammonium carbonate, zirconium hydrofluoride, ammonium zirconium fluoride, potassium zirconium fluoride, sodium zirconium fluoride, zirconium acetylacetonate, zirconium butoxide-1-butanol solution, zirconium n-propoxide and so on. The titanium compound includes titanium hydrofluoride, ammonium titanium fluoride, potassium titanium oxalate, titanium isopropoxide, isopropyl titanate, titanium ethoxide, titanium 2-ethyl-1-hexanolate, tetraisopropyl titanate, tetra-n-butyl titanate, potassium titanium fluoride, sodium titanium fluoride and so on. These compounds may be used alone or in a suitable combination.
The above-mentioned zirconium compound and/or titanium compound is formulated, in each liter of the metallic surface-treating agent, in a concentration of 0.01 to 50 g/l, preferably 0.05 to 5 g/l, in terms of zirconium ion or titanium ion. If the concentration of the above compound is less than 0.01 g/l, corrosion resistance will become insufficient. If it exceeds 50 g/l no improvement will be realized inprocessing adhesion and, in addition, the-bath stability will be rather sacrificed.
The metal surface-treating agent according to the invention comprises a thiocarbonyl group-containing compound and/or a water-soluble acrylic resin. The thiocarbonyl group-containing compound may be a compound having at least one thiocarbonyl group, thus including thiourea, dimethylthiourea, 1,3-dimethylthiourea, dipropylthiourea, dibutylthiourea, 1,3-diphenyl-2-thiourea, 2,2-ditolylthiourea, thioacetamide, sodium dimethyldithiocarbamate, tetramethylthiuram monosulfide, tetrabutylthiuram disulfide, zinc N-ethyl-N-phenyldithiocarbamate, zinc dimethyldithiocarbamate, pentamethylenedithiocarbamic acid piperidine salt, zinc diethyldithiocarbamate, sodium diethyldithiocarbamate, zinc isopropylxanthate, ethylenethiourea, dimethylxanthogen disulfide, dithiooxamide, polydithiocarbamic acid or it salt, and so on. These compoundstcan be used each independently or two or more of them may be used in a suitable combination.
The thiocarbonyl-containing compound mentioned above is formulated in a concentration of 0.01 to 100 g/L, preferably 0.1 to 10 g/L. If the concentration of the above compound is less than 0.01 g/L, the corrosion resistance will be insufficient, while the concentration in excess of 100 g/L will result in uneconomical use because of the saturation of corrosion resistance-improving effect.
The water-soluble acrylic resin is a copolymer based on acrylic acid and/or methacrylic acid and includes their copolymers with methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate, etc. inclusive of derivatives thereof, and other acrylic monomers. It is particularly preferable that acrylic acid and/or methacrylic acid account for not less than 70% of the total monomer constituting a copolymer. The acrylic resin is formulated in a concentration of 0.1 to 100 g/L in each liter of the metal surface-treating agent of the invention. When the concentration of the acrylic resin is less than 0.1 g/L, the bend adhesion and deep drawability cannot be sufficiently improved. On the other hand, the Concentration exceeding 100 g/L is uneconomical because of the saturation of improvement effect on bend adhesion and deep drawability.
The molecular weight of the acrylic resin is preferably not less than 10,000 on a weight average basis. The more preferred range is 300,000 to 2,000,000. Exceeding 2,000,000 will results in an excessively high viscosity to adversely affect workability.
The metallic surface-treating agent of the present invention may be supplemented with phosphate ion to thereby improve corrosion resistance.
The above addition of a phosphate ion can be made by adding a compound capable of forming a phosphate ion in water. As such compounds, there can be mentioned phosphoric acid; salts of phosphoric acid which are represented by Na3PO4, Na2HPO4 and NaH2PO4; and condensed phosphoric acid compounds such as condensed phosphoric acid, polyphosphoric acid, metaphosphoric acid, pyrophosphoric acid, ultraphosphoric acid, etc. and salts thereof. These compounds can be used alone or in a suitable combination.
The above phosphate ion is formulated in a concentration of 0.01 to 100 g/l, preferably 0.1 to 10 g/l per each liter of the metallic surface-treating agent. If the concentration is less than 0.01 g/l, the corrosion resistance-improving effect will be insufficient. On the other hand, exceeding 100 g/l is objectionable because the zinc type-coated steel materials will be over-etched to cause a degradation of performance or, when a water-based resin is contained as an additional component, it will cause gelation.
The metallic surface-treating agent of the present invention may further comprise other components. As such other components, there can be mentioned tannic acid inclusive of its salt, phytic acid inclusive of its salt, and water-based resin. The water-based resin which can be used includes urethane resin, epoxy resin, ethylene-acrylic copolymer, phenolic resin, polyester resin, polyolefin resin, alkyd resin and polycarbonate resin, among others. These water-based resins can be used each independently or in a suitable combination. When a water-based resin is used, an organic solvent may be used concomitantly for improving its film-forming properties to thereby provide a more uniform, smooth film. Furthermore, a leveling agent, a wetting agent and a antifoaming agent may also be used.
The metallic surface-treating agent of the present invention can be used as a surface treating agent for such steel substrates as cold-rolled steel, hot-rolled steel, stainless steel, electroplated zinc-coated steel, hot-dip zinc coated steel, zinc-aluminum alloy-coated-steel, zinc-iron alloy-coated steel, zinc-magnesium alloy-coated steel, zinc-aluminum-magnesium alloy-coated steel, aluminum-coated steel, aluminum-silicon alloy-coated steel, tin-coated steel, lead-tin alloy coated steel, chromium-coated steel; Ni-coated steel; etc., with particularly beneficial effects in the case of metal-precbated steel materials. The method of using this surface-treating agent, that is to say the method of treating a steel material surface, may comprise applying said metallic surface-treating agent to a substrate metallic surface and drying the coat or comprise heating such a substrate in advance, applying the metallic surface-treating agent of the invention and allowing the coat to dry by utilizing the residual heat of the substrate.
In both cases, the above drying procedure can be carried out at room temperature to 250xc2x0 C. for 2 seconds to 5 minutes. If the limit of 250xc2x0 C. is exceeded, adhesion and corrosion resistance will be adversely affected. Preferred conditions are 40xcx9c180xc2x0 C.xc3x975 seconds xcx9c2 minutes.
In the method of treating a metallic surface according to the present invention, the amount of deposition of said metallic surface-treating agent is preferably not less than 0.1 mg/m2 on a dry film basis. If the coverage is less than 0.1 mg/m2, the rust-preventive effect will be insufficient. On the other hand, if the coverage is excessive, it will be uneconomical as a pretreatment for coating. Therefore, the more preferred coverage is 0.5 to 500 mq/m2, particularly 1 to 250 mg/m2.
In practicing the method of treating a metallic surface according to the present invention, the mode of use of said metallic surface-treating agent is not particularly restricted. Thus, the routine techniques such as roller coating, shower coating, spray-coating, dipping and brush coating can be selectively employed. The optimum steel substrate includes metal-coated steel materials, particularly various plated steel materials.
The method of producing a coated steel material according to the present invention comprises treating a metallic surface with said metallic surface-treating agent, drying the coat, and applying a top coat. The top coat may for example be a top coat formed after the application and drying of a nonchromate primer or a functional coat formed for imparting such a function as fingerprint resistance or lubricity.
The above production technology can be applied not only to precoated steel materials but also to postcoated steel materials, and the xe2x80x9ccoated steel materialxe2x80x9d as referred to in this specification includes both types of steel materials. Furthermore, the term xe2x80x9csteel materialxe2x80x9d is used herein to mean any and all steel materials inclusive of steel sheets and plates.
The nonchromate primer which can be used may be any primer not containing a chromate type rust-preventive pigment in its formulation. The primer preferably contains a vanadate type rust-preventive pigment or a phosphate type rust-preventive pigment (V/P pigment primer), or preferably uses a calcium silicate type rust-preventive pigment.
The coating amount of said primer is preferably equivalent to adry thickness of 1 to 20 xcexcm. If the dry thickness is less than 1 xcexcm, corrosion resistance will be insufficient. If the thickness exceeds 20 xcexcm, processing adhesion will not be sacrificed.
The baking conditions for said nonchromate primer may be 150 to 250xc2x0 C., in terms of metal surface temperature, and a baking time of 10 seconds xcx9c5 minutes.
The top coating is not particularly restricted but may be any of the conventional top coatings.
The functional coating is not particularly restricted, either, but includes all kinds of coatings which are in use on chromate-pretreated surfaces.
The coating technology for said nonchromate primer, said top coat and said functional coat is not particularly restricted but includes roller coating, shower coating, air-spray coating, airless-spray coating and dip coating, among others.
The nonchromate metallic surface-treating agent according to the invention comprises a silane coupling agent and/or a hydrolytic condensation product thereof, a water-dispersible silica, a zirconium compound arid/or a titanium compound, and a thiocarbonyl-containing compound and/or a water-soluble acrylic resin. This metallic surface-treating agent is suit ed to the treatment of metals, particularly plated steel materials, and is capable of imparting excellent processability and corrosion resistance to the substrates for coating without enlisting the help of chromium.
Furthermore, by applying the metallic surface-treating agent of the invention to a process for producing nonchromate coated steel materials, the steel materials can be provided with processability, deep drawability and corrosion resistance equivalent or even superior to those of the conventional steel materials obtainable by using a chromate-containing rust-preventive agent.
The above advantages seem to come forth from the fact that since the metallic surface-treating agent of the present invention comprises a silane coupling agent, the reactive moiety of the silane coupling agent is firmly bound to the substrate metal surface through metasiloxane bonding and the organic moiety of the hydrophobic group is firmly bound to the organic film thereon to improve adhesion and thereby contribute to increased corrosion resistance. Moreover, particles of the water-dispersible silica are adsorbed and oriented on the substrate surface to act as a barrier against corrosive ions and moisture and thereby suppress corrosion, while the silanol group present on the silica surface enhances the adhesion between the organic film formed thereon and the metal surface. As to the zirconium ion, the formation of a zirconium oxide film on the metal surface-enhances corrosion resistance and, at the same time; the zirconium acts as a crosslinking agent for the film deposited thereon to increase the crosslinking density of the organic film to thereby further contribute to corrosion resistance, adhesion and coin scratch resistance. It is also considered that the thiocarbonyl-containing compound and the phosphate ion are readily adsorbed on the metal surface to cause a passivation of the metal surface and, moreover, their concurrent presence produces a synergistic effect leading to a marked improvement in corrosion resistance.
It is likely that as the acrylic resin acts as a binder for inorganic components such as dispersible silica, zirconium and the like, it contributes to improvements in the adhesion of the processed part and in deep drawability.
The coated steel material obtained in accordance with the present invention has excellent processability and corrosion resistance and, as such, finds application in a broad field of uses, such as household electrical appliances, computer-related devices, architectural members, and automotive and other industrial products.